The present invention relates to tank pressure control systems and particularly to an apparatus for controlling flow of fuel vapor and liquid fuel through an aperture in a fuel tank. More particularly, the present invention relates to a tank venting control assembly that closes automatically to prevent discharge of fuel vapor and liquid fuel from the fuel tank during refueling, agitation of the tank, or vehicle rollover, while opening automatically to allow discharge of fuel vapor with minimum discharge of liquid fuel during normal operation of the vehicle.
Controlling fuel vapor pressure in vehicle fuel tanks has long been an objective for automobile manufacturers and suppliers of fuel systems components. Fuel vapor can be created in the fuel tank by temperature differences between the fuel tank and liquid fuel from a fuel pump, as well as by sloshing and agitation of the fuel tank during normal vehicle operation. The pressure build-up resulting from the creation of new fuel vapors must be properly relieved. For this reason, some vehicle fuel systems are equipped with pressure relief valves capable of discharging a relatively large amount of fuel vapor through an outlet which is typically of relatively small diameter due to limitations on space available in the vicinity of the fuel tank.
Once the fuel vapor has been discharged from the fuel tank, the vapor must be adequately captured and stored to assure compliance with air pollution regulations. In some vehicle fuel systems, discharged fuel vapor is exhausted to a charcoal-filled vapor recovery canister designed to capture and store fuel vapor. These so-called "on-board" fuel vapor recovery systems are disclosed, e.g., in U.S. Pat. Nos. 4,770,677; 4,816,045; and 4,836,835.
The attempt to achieve high fuel vapor flow rates has spawned a number of collateral problems in the design of venting control assemblies for fuel systems. One major problem with high flow capacity closure assemblies is that they tend to allow liquid fuel carryover. That is, droplets of liquid fuel become entrained in fuel vapor upon sloshing or agitation of the fuel tank and are discharged through the discharge orifice.
Liquid fuel carryover is undesirable for a number of reasons. For instance, the liquid droplets can be deposited in the vapor recovery canister, where they are likely to impair the canister's effectiveness in capturing fuel vapor.
In addition, it has long been appreciated that venting control assemblies should provide means for preventing liquid fuel leakage during tilting or rollover of the vehicle (see, e.g., U.S. Pat. Nos. 4,351,350; 4,655,238; 4,760,858). However, venting control assemblies allowing discharge of high mass flow rates of fuel vapor should also provide means for reducing discharge of liquid fuel even when the fuel tank is in its normal, upright position.
Further, it is important that venting control assemblies provide means for rapidly adjusting between fuel vapor venting and fuel vapor retaining positions. For example, it may be important to adjust quickly from a fuel vapor venting configuration to a fuel vapor retaining position in response to a rapid change in operating conditions of the vehicle.
According to the present invention, an apparatus is provided for controlling flow of fuel vapor and liquid fuel through an aperture in a fuel tank. The apparatus includes a housing mounted in the aperture and formed to include a venting outlet, and means for selectively blocking discharge of fuel vapor and liquid fuel through the venting outlet. The blocking means is movable between a flow-blocking position closing the venting outlet and flow-delivery position opening the venting outlet.
The apparatus further includes first means for using pressurized fuel vapor in the fuel tank to move the blocking means from the flow-blocking position to the flow-delivery position. The using means includes a diaphragm appended to the blocking means for movement therewith. The diaphragm is movable between a first position allowing the blocking means to assume its flow-blocking position and a second position moving the blocking means to its flow-delivery position.
The apparatus further includes second means for using fuel vapor discharged from the fuel tank through the venting outlet to provide a pressure cushion acting against the diaphragm. The pressure cushion facilitates movement of the diaphragm from its second position to its first position, thereby minimizing the possibility that the blocking means will improperly remain in a flow-delivery position under conditions in which continued venting of fuel vapor is not desired.
In operation of the apparatus of the present invention during normal vehicle operation with the fuel cap installed on the filler neck, fuel vapor pressure is communicated to the diaphragm and builds up until it is sufficient to move the diaphragm from the first to the second position. Movement of the diaphragm to the second position in turn causes the blocking means to move to the flow-delivery position, thus allowing fuel vapor to vent through the venting outlet. Before this discharged fuel vapor is carried away to an outlet passageway, the fuel vapor momentarily accumulates in the second using means. As additional fuel vapor is accumulated, the fuel vapor pressure rises sufficiently to return the diaphragm to its first position. Advantageously, the second using means creates a pressure cushion underneath the diaphragm to insure that the diaphragm is able to return to its first position, thus allowing the blocking means to return to its flow-blocking position blocking discharge of fuel vapor through the venting outlet.
The apparatus also includes a venting control chamber in the housing and means for communicating fuel vapor from the fuel tank to the venting control chamber. The diaphragm is mounted so that a portion of the diaphragm is exposed to pressure extant in the venting control chamber. Pressurized fuel vapor can travel from the fuel tank into the venting control chamber through the communicating means. Whenever the pressurized fuel vapor extant in the venting control chamber has a pressure in excess of a predetermined threshold level, that Pressure will apply a force to the diaphragm causing the blocking means to move to its flow-delivery position opening the venting outlet. As a result, pressurized fuel vapor in the fuel tank is able to escape from the fuel tank through the venting outlet.
In preferred embodiments, the apparatus also includes a float valve buoyantly supported in liquid fuel introduced into the fuel tank and arranged to block flow of pressurized fuel vapor from the fuel tank into the venting control chamber through the communicating means. The float valve is configured to move to a position closing the communicating means upon accumulation of a sufficient volume of liquid fuel in the fuel tank. The float valve is also configured to function as a rollover valve so that it is able to move to a closed position to block flow of liquid fuel through the communicating means at least during rollover of a vehicle containing the fuel tank.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.